Neurones in the spinal trigeminal nucleus of the cat responding to movement of the vibrissae.

1. In chloralose anaesthetised cats the receptive field organisation and response properties of neurones of the spinal trigeminal nucleus were exmained and compared with the discharge characteristics of afferent units from vibrissae. 2. The response properties of the primary afferent discharges were preserved in at least a proportion of the second order cells, 82% of those which responded to movements of the maxillary vibrissae had phasic discharges and 18% had tonic discharges. 3. The discharge characteristics of the two main types of primary afferent slowly-adapting units (St I and St II) were distinguishable in the tonically active cells of the nucleus. These two groups showed (i) substantially different interspike interval distributions, (ii) different adaptive properties and (iii) different directional sesitivity. The two categories were designated nuclear type I and type II in accordance with the classification of primary afferent slowly-adapting units. 4. A loss of stimulus information was deduced from a consistent increase in the variability of the second order discharges compared with their presumed afferent input, but this information loss may be important in allowing the linear summation of discharges at the level of the thalamus.